I just got the 8 series, and trying to figure out how to get Dolby Atmos sound with my Apple TV 4K. And both of my HDMI cords are Ultra Premium, so capable of Atmos, eArc, VRR etc.
So for the TV settings, I enabled CEC, and it shows that the eARC is available for HDMI 4, which is connected to my Sonos Arc, and it shows that it’s “active” but puts an “*” at the end of it, so not sure what that means.
And when I check the audio output, the choices are: Auto Detect, Auto Passthrough, Dolby Digital, Dolby Digital Plus... but not a choice for Dolby Atmos.
When I play 4K movies on my Apple TV 4K that have Dolby Atmos, the setting on the TV shows that the sound is DTHD. And most times watching Hulu or other streaming apps (all via Apple TV), it typically shows audio output as PCM.
So the last thing I checked was Netflix through the TV directly, and when I played a movie that was both Dolby Vision and Atmos, the sound did show that it was in fact playing in Atmos.